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/**
* Copyright (C) 2023-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include <vector>
#include "mongo/db/pipeline/percentile_algo.h"
namespace mongo {
/**
* 'DiscretePercentile' algorithm for computing percentiles is accurate and doesn't require
* specifying a percentile in advance but is only suitable for small datasets. It accumulats all
* data sent to it and sorts it all when a percentile is requested. Requesting more percentiles
* after the first one without incorporating more data is fast as it doesn't need to sort again.
*/
class DiscretePercentile : public PercentileAlgorithm {
public:
DiscretePercentile() = default; // no config required for this algorithm
void incorporate(double input) final;
void incorporate(const std::vector<double>& inputs) final;
boost::optional<double> computePercentile(double p) final;
std::vector<double> computePercentiles(const std::vector<double>& ps) final;
long memUsageBytes() const final {
return _accumulatedValues.capacity() * sizeof(double);
}
protected:
std::vector<double> _accumulatedValues;
// While infinities do compare and sort correctly, no arithmetics can be done on them so, to
// allow for implementing quick select in the future and to align with our implementation of
// t-digest, we are tracking them separately.
int _negInfCount = 0;
int _posInfCount = 0;
bool _shouldSort = true;
};
} // namespace mongo
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